Laboratory muffle



April 2' E. B; FORSE- K 1,710,870

'LABORATORY MUFFLE v Filed Sept. 1927 M 1 J. H J."

INVENTOR Patented Apr, 30, 1929.

. UNITED STATES PATENT OFFICE.

EDWIN I. FORSE, OF METUCHEN, NEW JERSEY, ASSIGNOB TO THE CARBORUNDUM COMPANY, OF NIAGARAFALLS, NEW YORK, A CORPORATION -01? PENNSYLVANIA.

LABORATORY MUFFLE.

I Application filed September 2, 1927. Serial No. 217,074.

This invention is for a mufile or other heating chamber for use in connection with certain metallurgical operations, and relates more especially to a muffle for laboratory use 5 for receiving crucibles or cupels.

The metallurgical laboratories of smelting companies use large number of assay mutlles for heating crucibles and cupels. During the ast few. years, muffles have been manulu actured of silicon carbide instead of fireclay. The silicon carbide muflies ive a much longer life due to their freedom rom cracking and because of the high refractory properties of silicon carbide. On account of the high thermal conductivity and heat permeability of silicon carbide, the analyst has been able to carry through the. operation much more quickly and with less expenditure of fuel than is'necessary with the usual type of fire clay muffle. i

One difficulty which has been encountered with silicon carbide mufiles is that in some operations, certain substances react with the silicon carbide to disintegratethe walls thereof. For instance, in some operations, lead oxide is given off, and this substance combines very actively with silicon carbide, and decom-' poses it. The result is that where a group of cupels are placed in a mufile, the vapors of lead oxide which arise from each cupel, will decompose a spot in the roof of the muflie above each cupel, and will sometimes bore a small hole right through the silicon carbide roof above each cupel. v

.To overcome this difliculty the present invention proposes to. make a composite mufile having the walls least subject to attack formed of silicon carbide and having the walls which are most rapidly disintegrated by reaction with materials in the muffle made from some material which is resistant other refractory to the fumes arising from the cupels. As an example, where lead oxide is given off from cupels in the muflle, the sides and bottom are of silicon carbide, while the top is of a material resistant to lead oxide. One material which has been used with great success for the roof of a muflie where lead oxide is given off, is fused crystal alumina, such as is produced in largequantities for abrasive pnrposes and for refractory purposes. The action of lead oxide and other fumes which are given off in the cupelling operations, have very little action on fused alumina, and this form of composite muflle combines the advantages derived from the. use of silicon carbide with the resistant properties of fused alumina and other substances, and thereby provides a mufile whose life will be greatly prolonged.

The invention may be readily understood by reference tothc accompanying drawings in which Fig. 1 represents a vertical transverse section through one form of muffle embodying my invention;

Fig. 2 shows such a muffle partly in section and partly in side elevation;

Fig. 3 is a View similar to Fig. 1 of a slightly modified form of muflle;

Fig. 4 is a view similar to Fig. form of mufile shown in Fig. 3;

Fig. 5 is a view similar to Fig. 1 of still another slightly modified form.

Fig. 6 is a View similar to Fig. 5 wherein the bottom of the muffle ismore resistant than the sides and top thereof.

The inufile shown in Figs. 1 and 2 has a'bottom 2, side walls 3 and an end wall 4, and all of these walls are formed of silicon carbide. According to a preferred embodiment of the invention, the silicon carbide mix consists of 90 parts of silicon carbide grains of graded fineness, 8 parts of fire clay and 6 arts of temporary binder. This is thorough y mixed together until it has the consistency of an ordinary molding sand.

2, of the Over the top of the mufile is a roof 5 which is formed of some material more resistant to the fumes rising out of the cupels than is silicon carbide. This material is preferably formed of fused alumina, and the mixture from which it is formed-preferably contains 85 parts of fused alumina grains of graded fineness, 15 parts of fire clay, and 2.7 parts of temporary binder, This mixture is thoroughly mixed and brought to the consistency of molding sand.

In the construction shown in Fig. 1, the top 5 is formed separately, the sides 3 having a tongue 3* which overlaps a tongue 5 on the top section. -The top is thus fitted onto the body of the muflle. By reason of the muffie beingformed of two parts, no strain is set up in the walls due-to differences in the coefficients of expansion in the materials of which the sides and top are composed. Also, either part may be replaced, when necessary. In the form of muflie shown in Figs. 3 and 4, the muflle has abottom 6, sides 7, end 8, and a top 9. The bottom, sides, and end are formed of silicon carbide ,whiletheroof is formed of somesubstance more resistant to the fumes risin out of the cupels than is silicon carbide. T is may be the material above mentioned,'. or any other suitable material.

, In this form of mufile, the roof'or top 9, is

is of silicon carbide. The joint between the material of the top and that of the sides is unevenor ragged, so as to secure the best possible' cohesion, and avoid the formation of any straight'line of fracture between the two materials. With careful selection of mate rials and careful molding, cracking of the muflle by reasons of differences in this coeflicients of expansion of the two materials,

either in the initial firing, or subsequent use thereof, 1s avoided.

The .muflle or .chamber shown 1n Fig. 6

shows the materials reversed. The bottom 12 is'of fused alumina or other resistant refractory while the body 13of the chamber is of silicon carbide. This form is used where the bottom of the mnflle or chamber is most likely to react with substances in the chamber.

Instead of using a fused alumina, other neutral or basic refractory materials may be used for the resistant portion of the mufile.

For instance, fire clays of the kaolin type can be used, as well as fire clays high in alumina, sillimanite,magnesite, and fused ma esia.

The advantages of the invention arise out of the provision of one portion of the muffle or other chamber which is more resistant to the fumes coming out of the cupels or to other materials in the mufiles than is silicon car'- bide, while'rthe body of the mufile may still becomposed of silicon carbide and the advantages of silicon carbide thus retainedin While I have illustrated and described particular embodiments of my invention, it will be understood that the invention may be otherwise embodied, and that various changes and modifications may be made within the spirit of my invention and under the scope of the following" claims.

I claim: Y

1. A heating chamber for metal recovery whichmostof'the heat is operations whose walls are comprised of at a least two sections, one of which is of silicon carbide while the other is comprised of a refractory metallic oxide material, the latter forming tliatvpa'rt of the structure which is more directly exposed to the action of oxidizing or easily reducible materials in the chamber, the former constituting the part throu h transmitted to e chamber. I

2. Amuflle'forcupelling operations comprising a .main body portion having a bottom andsides composed of a material possessing a thermal conductivity at least three times that of fireclay and a roof for the mufile formed of a refractory metallic oxide more resistant to the fumes arising from the cupels than is the body of the mufile. 4 I

3. A cupelling muffle comprising a body portion composed of bonded granular silicon carbide and having a roof portion composed of neutral or basic refractory resistant to the action of lead oxide.

4. A cupelling mufile having a main body portion formed of bonded granular silicon carbide and having a refractory top'more resistant to:decomposition by lead oxide than silicon carbide. I 5. A cnpelling muffle. composed of a main body portion formed of bonded granular silicon carbide, and having a section which is composed of bonded fused alu'minus oxide. '6. A- cupelling mufile comprising a main body" portion composed of bonded granular silicon carbide, and a separate roof section composed of a neutralor basic refractory.

7 A muflle for use in metal recovery operations having a'rmain bodyportion which is composed of a material having a thermal conductivity more than three times that of fire clay and having the remaining portion there of composed of refractory metallic oxides which .are substantially nonreactive with respect to the metallic oxides and vapors given off inmetal recovery operations.

EDWIN B. FORSE. 

